Geochemical Determination of Calcareous Gravel Provenance by Analogy to Archeological Marble Provenance Studies

The provenance of foreland basin-fill sediments is a key tool for reconstructing the evolution of the basin's associated mountain belt. However, mountain belts containing thick carbonate successions (e.g., Pyrenees, Apennines) will yield sediments whose provenance is difficult to interpret with much specificity, impairing the study of the orogens' evolution. This is due both to the low lithologic diversity of the source region and to the susceptibility of carbonates to chemical diagenesis during surface exposure. We argue that determining carbonate clast provenance is analogous to determining that of marbles used in ancient architecture and statuary, which is done by statistical analysis of various geochemical variables including δ¹³C, δ¹⁸O, and spectroscopy-derived trace element information. We apply techniques similar to those used for marble provenance to carbonate gravel deposited on the southeastern margin of the Ebro Basin (northeastern Spain), in alluvial fan conglomerates known to derive from the nearby Catalan Coastal Ranges (CCR). Samples from throughout the CCR carbonate succession and gravel from conglomerates in the lower and upper Ebro conglomerate succession have been analyzed by gas source mass spectrometry for δ¹³C and δ¹⁸O and by ICP-AES for trace element concentrations. The good agreement of basin and CCR samples in [Mn], [Fe] and Sr/Ca ratio, proxies for carbonate diagenesis, suggests that little provenance-obscuring diagenesis has affected the basin gravel. Discriminant analysis using the measured geochemical variables suggests, contrary to earlier petrographic provenance studies, that material from the lowest part of the CCR carbonate succession was contributed to the basin from the earliest onset of conglomerate deposition, and that the proportion of this deep source material increases with height in the basin section – yielding a normal unroofing sequence. These results demonstrate the feasibility of geochemical provenance analysis for carbonate clasts and its usefulness for reconstructing the evolution of carbonate-rich regions such as the CCR.